The use of holy water in the earliest days of the Christian Era is attested by documents of only comparatively late date. The "Apostolic Constitutions", the redaction of which goes back to about the year 400, attribute to the Apostle St. Matthew the precept of using holy water. The letter written under the name of Pope Alexander I, who lived in the second century, is apocryphal and of more recent times; hence the first historical testimony does not go back beyond the fifth century. However, it is permissible to suppose for the sake of argument that, in the earliest Christian times, water was used for expiatory and purificatory purposes, to a way analogous to its employment under the Jewish Law. As, in many cases, the water used for the Sacrament of Baptism was flowing water, sea or river water, it could not receive the same blessing as that contained in the baptisteries. On this particular point the early liturgy is obscure, but two recent discoveries are of very decided interest. The Pontifical of Scrapion of Thumis, a fourth-century bishop, and likewise the "testamentum Domini", a Syriac composition dating from the fifth to the sixth century, contain a blessing of oil and water during Mass. The formula in Scrapion's Pontifical is as follows: "We bless these creatures in the Name of Jesus Christ, Thy only Son; we invoke upon this water and this oil the Name of Him Who suffered, Who was crucified, Who arose from the dead, and Who sits at the right of the Uncreated. Grant unto these creatures the power to heal; may all fevers, every evil spirit, and all maladies be put to flight by him who either drinks these beverages or is anointed with them, and may they be a remedy in the Name of Jesus Christ, Thy only Son." As early as the fourth century various writings, the authenticity of which is free from suspicion, mention the use of water sanctified either by the liturgical blessing just referred to, or by the individual blessing of some holy person. St. Epiphanius (Contra haeres., lib. I, haer. xxx) records that at Tiberias a man named Joseph poured water on a madman, having first made the sign of the cross and pronounced these words over the water: "In the name of Jesus Christ of Nazareth, crucified, depart from this unhappy one, thou infernal spirit, and let him be healed!" Joseph was converted an subsequently used the same proceeding to overcome witchcraft; yet, he was neither a bishop nor a cleric. Theodoret (Hist. eccl., V, xxi) relates that Marcellus, Bishop of Apamea, sanctified water by the sign of the cross and that Aphraates cured one of the emperor's horses by making it drink water blessed by the sign of the cross ("Hist. relig.", c. viii, in P.G., LXXXII, col. 1244, 1375). In the West similar attestations are made. Gregory of Tours (De gloria confess., c. 82) tells of a recluse named Eusitius who lived in the sixth century and possessed the power of curing quartan fever by giving its victims to drink of water that he had blessed; we might mention many other instances treasured up by this same Gregory ("De Miraculis S. Martini", II, xxxix; "Mirac. S. Juliani", II, iii, xxv, xxvi; "Liber de Passione S. Juliani"; "Vitae Patrum", c. iv, n. 3). It is known that some of the faithful believed that holy water possessed curative properties for certain diseases, and that this was true in a special manner of baptismal water. In some places it was carefully preserved throughout the year and, by reason of its having been used in baptism, was considered free from all corruption. This belief spread from East to West; and scarcely had baptism been administered, when the people would crown around with all sorts of vessels and take away the water, some keeping it carefully in their homes whilst others watered their fields, vineyards, and gardens with it ("Ordo rom. I", 42, in "Mus. ital.", II, 26).

However, baptismal water was not the only holy water. Some was permanently retained at the entrance to Christian churches where a clerk sprinkled the faithful as they came in and, for this reason, was called hydrokometes or "introducer by water", an appellation that appears in the superscription of a letter of Synesius in which allusion is made to "lustral water placed in the vestibule of the temple". This water was perhaps blessed in proportion as it was needed, and the custom of the Church may have varied on this point. Balsamon tells us that, in the Greek Church, they "made" holy water at the beginning of each lunar month. It is quite possible that, according to canon 65 of the Council of Constantinople held in 691, this rite was established for the purpose of definitively supplanting the pagan feast of the new moon and causing it to pass into oblivion. In the West Dom Martène declares that nothing was found prior to the ninth century concerning the blessing and aspersion of water that takes place every Sunday at Mass. At that time Pope Leo IV ordered that each priest bless water every Sunday in his own church and sprinkle the people with it: "Omni die Dominico, ante missam, aquam benedictam facite, unde populus et loca fidelium aspergantur" (P.L., CXV, col. 679). Hincmar of Reims gave directions as follows: "Every Sunday, before the celebration of Mass, the priest shall bless water in his church, and, for this holy purpose, he shall use a clean and suitable vessel. The people, when entering the church, are to be sprinkled with this water, and those who so desire may carry some away in clean vessels so as to sprinkle their houses, fields, vineyards, and cattle, and the provender with which these last are fed, as also to throw over their own food" ("Capitula synodalia", cap. v, in P.L., CXXV, col, 774). The rule of having water blessed for the aspersion at Mass on Sunday was thenceforth generally followed, but the exact time set by Leo IV and Hincmar was not everywhere observed. At Tours, the blessing took place on Saturday before Vespers; at Cambrai and at Aras, it was to be given without ceremony in the sacristy before the recitation of the hour of Prime; at Albi, in the fifteenth century, the ceremony was conducted in the sacristy before Terce; and at Soissons, on the highest of the sanctuary steps, before Terce; whereas at Laon and Senlis, in the fourteenth century, it took place in the choir before the hour of Terce. There are two Sundays on which water is not and seems never to be blessed: these are Easter Sunday and Pentecost. The reason is because on the eve of these two feasts water for the baptismal fonts is blessed and consecrated and, before its mixture with the holy chrism, the faithful are allowed to take some of it to their homes, and keep it for use in time of need.